OSPF packet lab doubt

[Umesh Prajapati11238]

Hi all,

Today I was doing lab in ospf in order to check packet's details, let me show you the topology.

As per the topology R2 router should become the master router and slave will be R1 router because both router's priority is same for example 1, R2 router's router Id is higher than R1 then R2 will become  master right.

My question  is the if R2 router will be master then R2 router will start to exchange information with its neighbors here is neighbor R1. but when I captured packet then I saw R1 router is sending request to R2 router why.

Please find the also wireshark packet caputre what I have taken.

PFA - wireshark snapshot too.

Please do reply my question,

Thank you

[MHM Cisco World]

check the comment below 

[David Ruess]

Hello,

I think you have some terminology messed up but other than that it looks to be functioning normally.

1. I think what you're refereeing to as Master/Slave is actually DR/BDR. I say thing because OSPF has a separate unrelated process for choosing Master/Slave relationships that control sequence numbers of updates. If you are in fact talking about the Master/Slave relationship then its just for really who is in charge of sending first. They will still send messages to each other. "The master controls the synchronization process and ensures that only one DD packet is outstanding at a time. "

2. The process you have highlighted looks to be working as intended. You are using an Ethernet link so it will elect R2 as you say as the DR and R1 as the BDR. In normal function the DR and BDR will form full adjacency with each other and exchange LSDB. If R2 is the only device allowed to send updates how will R2 know about R1 routes? OSPF requires all devices in the same area have the same LSDB so all devices need to exchange routes with each other. 

3. If you look R1 and R2 exchange LSDB information with each other. Then after everything calms down R1 starts sending packets to the OSPF DR address of 224.0.0.6 which is R2 and R2 sends packets/updates to the OSPF ALL routers address of 224.0.0.5.

P.S. @MHM Cisco World I dont think the DR/BDR election has influence on Master/Slave. They are separate processes that work even on media with no DR/BDR so the Master/Slave relationship works irrespective of DR/BDR election. I'd have to check though.

Hope this helps.

-David

[MHM Cisco World]

check the comment below 

[David Ruess]

I don't think that is correct. The router ID is solely responsible for the Master/Slave relationship, not priority. They are separate processes. The Master/Slave relationship uses a "similar" process to DR/BDR election but its not the same. Your statement said that DR/BDR election overrides the Master/Slave election. I was just pointing out that while they use the similar mechanism, you can influence the DR/BDR but you cannot influence the Master/Slave. They can be different from each other.

[MHM Cisco World]

check the comment below 

[MHM Cisco World]

@Umesh Prajapati11238 
are you sure that OSPF use the Router-ID you specify under the OSPF process??

[MHM Cisco World]

@David Ruess @Umesh Prajapati11238 
R1-R2
R1 router-ID 1.1.1.1/32 and priority is 200 
R2 router-ID 2.2.2.2/32 and priority is default 

the DR/BDR election result DR is R1 and BDR is R2 
the master (depend only in Router-ID not priority)  is R2 and slave is R1 

in your case the issue that the router use the interface IP as router-ID not the manual Router-ID config under ospf, because the router-id manually add need restart ospf process.